1. Field of the Invention
The present invention relates to optical waveguides based on a photochromic diarylethene polymer, and to a method for the preparation thereof.
2. Description of the Related Art
As reported for instance by Yoshida et al., Journal of Photochemistry and Photobiology A: Chemistry 95 (1996) 265–270, materials the refractive index of which can be changed have been studied for optical applications. The refractive index change Δn in organic photochromic compounds have led to proposals for their use in a number of optical wave-guide components since a refractive index change in an optical wave-guide can shift the phase of the signal light. In addition, the reversible refractive index change of photochromic compounds allows the light phase shift to be controlled. However, almost all conventional organic photochromic compounds have low thermal stability, and the refractive index change caused by light irradiation is unstable at room temperature. Thermally irreversible photochromic compounds such as 1,2-diarylethene derivatives have been developed and good durability has been reported in photochromic reaction cycles. Once closed such 1,2-diarylethene derivatives are thermally stable but exhibit reversible photochromism with high conversion efficiency.
The above cited paper shows the performance of a number of compounds, for example
dispersed in PMMA (polymethylmethacrylate) at concentrations varying from 5 to 50 wt % against PMMA. A Δn of more than 10−3 was obtained with large compound concentration (higher than 30 wt %) only.
FR 2774998 (in the name of Ecole Polytechnique) relates to 1,2-dithienylethene compounds and polymers of general formula
wherein X and Y can be a reactive function such as COCl; R can typically be CH3, and R′ can be a cyclic group, typically —CF2CF2CF2—.
The photochromic materials can be constituted either by a solid matrix and photochromic molecules chemically bound to said matrix. Such chemical bond is said to obviate problems of phase separation occurring when the photochromic molecule is merely dispersed into the polymer matrix.
JP 11202144 (in the name of Hitachi Ltd.) discloses X-type wave-guides obtained by using at least two kind of photoactive diarylethene molecules (reactive at different wavelengths) dispersed in a polymeric matrix such as fluorinated PMMA. Irradiation is conducted through an exposure mask. Connection with optic fibers is also shown.
JP2000221351 (in the name of Kyocera Corp.) relates to an X coupler obtained by fluorinated PMMA containing photochromic diarylethene derivatives.